The path computation element (PCE) is an entity proposed by the Internet Engineering Task Force (IETF) for computing network paths or routes and applying computation constraints in the Multi-Protocol Label Switching (MPLS)/Generalized Multi-Protocol Label Switching (GMPLS) network. A PCE entity can be a network node, a stand-alone server, or a dedicated computing platform having the resource perception capability and multi-constraint complex computation capability.
Communication is conducted between the Path Computation Client (PCC) and the PCE and between the PCEs through the PCE Communication Protocol (PCEP). RFC5440 described the architecture of the PCEP protocol, the transmission layer of the PCEP protocol uses the Transmission Control Protocol (TCP), and two parties in the PCEP communication establish a PCEP session based on the TCP connection.
The PCE can compute paths in a single domain or multiple domains. In a single-domain domain, the Open Shortest Path First (OSPF) protocol can be used to flood the topology information and to form the Traffic Engineering Database (TED) in the local domain, and then the PCE performs a single-domain path computation based on the TED. Between the multiple domains, the Domain to Domain Routing Protocol (DDRP) can be used to flood the topology information and to form the inter-domain topology TED, and then the PCE performs a multi-domain path computation based on the TED.
If the capability of a single PCE is not sufficient to undertake a lot of path computation requests, it needs to introduce multiple PCEs, these PCEs have similar processing capabilities. If it needs to improve the performance of path computation in the network, these PCEs need to balance loads of a large number of path computation requests, that is, each PCE has to undertake part of the path computation tasks to achieve the purpose of load balancing. RFC4655 gives the concept of PCE load balancing, that is, different PCEs are selected to compute the path to achieve the purpose of load balancing, but do not provide an appropriate method.